Multiple gas lift production



March 10,1959 w. c. CARLISLE ETAL MULTIPLE GAS LIFT PRODUCTION 5Sheets-Sheet l Filed Dec. 10, 1956 y m a W. gm w. Z f6 a iii, /////4/////p// ///4 7 f d 0a A Z Mai-ch 10, 1959 v w. c. CARLISLE ETAL 2,876,703

MULTIPLE GAS LIFT PRODUCTION Filed Dec. 10, 1956 3 Sheets-Sheet 2 A77'0/P/VE VJ w. c, CARLISLE ETAL 2,876,703

MULTIPLE GAS LIFT PRODUCTION March 10, 1959 Y 5 Sheets-Sheet 3 FiledDec. 10, 1956 v INVENTORS MULTIPLE GAS LIFT PRODUCTION Willis C.Carlisle, John H. McCarvell, and Theodore R. Stalder, Houston, Tex.,assignors to Macco Oil Tool "Company, Inc., Houston, Tex., a corporationApplication December 10, 1956, Serial No. 627,498

Claims. (Cl. 103-4) This invention relates to multiple production of oilor other liquid with gas lift valves.

This application is a continuation-impart of United States patentapplication Serial No. 616,499 filed October 17, 1956. now abandoned.

An obiect of this invention is to provide a new and improved method andapparatus for producing oil or other liquid from a plurality of wellformations by using a plurality of gas lift valves which are suppliedwith gas from a common reservoir.

Another obiect of this invention is to provide a new and improved methodand apparatus for producing oil or other liquid from a plurality of wellformations, wherein each formation is produced through a separate pipestring, and wherein the fluid level in each pipe string controls theadmission of gas thereto for effecting the lifting of the oil or otherliquid with the gas.

A further object of this invention is to provide a new and improvedmethod and apparatus for producing oil or other liquid from multipleformations through concentric pipe strings positioned in a well casingwherein gas under pressure is provided in the casing annulus from thesurface, a gas-producing well formation, or any other gas pressuresource, and wherein the gas is directed to a fluid operated gas liftvalve on each of said pipe strings for admitting the gas separately toeach pipe string while avoiding intermingling of the oil or other liquidin the two strings.

Still another object of this invention is to provide a new and improvedmultiple production assembly in which one of a plurality of pipe stringshas a gas lift valve positioned internally thereof and another of thepipe strings has a gas lift valve positioned externally thereof, and inwhich both of the valves are in communication with a common source ofgas under pressure.

A still further object of this invention is to provide a new andimproved multiple production assembly wherein concentric pipe stringsare disposed in a well casing with means being provided for sealing anarea between the inner and the outer pipe strings for directing gas flowto the inner pipe string from the casing annulus, and with other meansbeing provided to by-pass the oil flow in the outer pipe string aroundthe area sealed oif to thereby maintain the gas flow to the inner pipestring separate from the fluid conditions in the outer pipe string.

The construction designed to carry out the invention will be hereinafterdescribed, together with other features thereof.

The invention will be more readily understood from a reading of thefollowing specification and by reference to the accompanying drawingsforming a part thereof, Wherein an example of the invention is shown,and wherein:

Fig. 1 is a diagrammatic view illustrating the apparatus of thisinvention in use for carrying out the method of this invention.

Figs. 2A and 2B are views, partly in elevation and partly in section,which together illustrate the upper portion of the assembly shown inFig. 1, and particularly that portion which includes the gas lift valvedisposed within the inner pipe string.

Fig. 3 is a horizontal sectional view taken on line 3--3 of Fig. 2B.

Fig. 4 is a view, partly in section, illustrating the details of the gaslift valve mounted on the outer pipe string.

Fig. 5 is a diagrammatic view similar to Fig. 1, but illustrating theassembly in position for triple production.

Fig. 6 is a cross-sectional view taken on line 66 of Fig. 5.

Fig. 7 is a cross-sectional view taken on line 7-7 of Fig. 5.

In the drawings, the letter P designates the inner one of the pipestrings. For dual well production, a second pipe string P-1 surroundsthe inner pipe string P, and both of such pipe strings P and P1 arepositioned in a well bore or casing W. It is to be understood that theterm well bore as used herein includes an open well bore or one having aWell casing therein. Well packers X and Y of conventional constructionare positioned in the well bore or casing W to provide longitudinallyspaced fluid seals in the annulus surrounding the pipe string P-l.Another well packer Z which is also of conventional construction ispositioned in the annular space between the pipe string P and the pipestring P-l. The lower end of the pipe string P is provided withperforations or openings 10, and the lower end of the pipe string P-l isalso open so that oil or other liquid from the well formation F passesupwardly into the interior of the pipe string P. Similarly, the pipestring P-l is provided with perforations or openings 12 above the packerZ and between the packers X and Y so that oil or other liquid from thewell formation F-l can flow through the perforated casing or well bore Wand into the annular space between the pipe strings P and P-l. The pipestring P has one or more gas lift valves V mounted therewith, andsimilarly, the pipe string P-i has one or more gas lift valves V1mounted therewith so that gas under pressure may be supplied from thecommon reservoir of the well bore annulus to either of the pipe stringsP or P-l separately as required to facilitate the lifting of the oil orother liquid therein, as will be explained in detail.

Considering the invention in detail, the pipe string P extends from thesurface of the well, and as explained above, such pipe string P has oneor more gas lift valves V mounted thereon. As shown in Figs. 2A and 28,a sealing element 15 formed of a plurality of rubber sealing rings 16,or any other annular sealing material, is provided on the externalsurface of the pipe string P above the location of one of the gas liftvalves V. Another sealing element 18 formed of resilient annular sealrings 19 made of rubber or other sealing material is positioned on theexternal surface of the pipe string P below the valve V. An opening orinlet passage 22 is provided in the pipe string P between the uppersealing element 15 and the lower sealing element 18 for establishingcommunication with the interior of the gas lift valve V, the details ofwhich will be explained hereinafter in connection with the gas liftvalve V-l. Although various types of gas lift valves may be used in thisinvention, it is preferable to use gas lift valves of the general typedisclosed in United States Patent No. 2,610,644 granted to W. C.Carlisle and J. H. McCarvell on September 16, 1952, wherein a gas liftvalve is disclosed which has a check valve therewith, and which isoperable to admit gas into the pipe string when a predetermined head orheight of oil or other liquid develops in the pipe string. Thus, withthe valve V, the gas is admitted into the interior of the pipe string Pthrough the inlet opening or passage 22 for discharge into the oil orother liquid in the pipe string P through the openings 24 of the valveV.

The pipe string P-l is formed with a by-pass sleeve 25 which extendslongitudinally within the pipe string P-l a distance suflicient toproject above and. below the sealing elements and 18 so that the sealingelements 15 and 18 may seal with the internal surface of such sleeve 25,as will be more evident hereinafter. The bypass sleeve is mounted in thepipe string P-l with circumferentially spaced lugs 26 at the upper endof the sleeve 25 and similarly spaced lugs 27 at the lower end of thesleeve 25. Preferably, the lugs 26 are welded or otherwise secured tothe inside of the pipe string P-1 and the internal surfaces of the lugs26 and 27 are welded or otherwise secured to the external surface of thesleeve 25. With such construction, fluid in the pipe string P-l may flowbetween the sleeves 25 and the internal surface of the pipe string P4,and since the lugs 26 and 27 are circtunferentially spaced (as best seenin Fig. 3), such lugs do not interfere with such flow of fluid. Theupper end 25a of the sleeve 25 is tapered downwardly and inwardly, andeach of the lugs 26 has a similarly tapered surface 26a forming acontinuation of the tapered surface 25a so as to guide the inner pipestring P into the sleeve 25. The lower end 25b of the sleeve 25 and thesurfaces 27a of the lugs 27 are tapered upwardly and inwardly to alsofacilitate the guiding of well tools which may be moved upwardly withinthe pipe string P4.

One of the valves V-l which is mounted on the pipe string P-l isillustrated in Fig. 4. Such valve V1 illustrated in Fig. 4 is typical ofthe type of valve which is used in the apparatus of this invention. Thepipe string P-l is provided with an opening 30 adjacent the gas liftvalve V-1 for the admission of the gas from the casing or well boreannulus into the annular space 31 between the pipe string P and the pipestring P-1. As previously stated, the valves V and V1 are preferably ofthe type disclosed in U. S. Patent 2,610,644. Thus, the valve V-1illustrated in Fig. 4 includes a housing or cap 32 which is welded orotherwise secured to the external surface of the pipe string P-l. Acoupling 33 is threaded or otherwise connected to the lower end of thehousing or cap 32, and a valve seat 34 is threaded or otherwiseconnected to the coupling 33. The valve seat 34 is formed or connectedat the lower end of a valve body 35 in which the valve member 36 ispositioned for seating on the valve seat 34. The valve 36 is urged toits seated or closed position by a coil spring 37 which works inconjunction with fluid under pressure contained in a chamber 33 formedby a bellows 39. The body 35 has an opening 35a which is aligned with anopening 32a and the opening 30 for directing the flow of gas from theinterior of the valve V-1 to the area or annular space 31 between thepipe strings P and P-l. The pressure in the pressure chamber 38 issupplied through an opening 38:: which is closed by a removable threadedcap 49 so that the valve 36 is maintained in its seated position on thevalve seat 34 until a predetermined head or height of the liquid in thepipe string P-l is developed. Thus, when the height of the liquid in theannular space 31 of the pipe string P-1 reaches a predetermined level,it exerts a force or pressure upwardly on the valve 36 to move sameupwardly and oil the seat 34 to open the passage 33a and to admit gasinto the annular space 31 through the opening 30. When the height of theliquid in the annular space 31 falls below such predetermined level, thepressure in the chamber 38, along with the spring pressure 39 act toclose the valve 36 so that gas is no longer admitted to the annularspace 31.

A check valve body 41 is mounted below the coupling 33 and is threadedor otherwise connected thereto. The check valve 42 is disposed Withinthe body 41 and is adapted to seat on a valve seat 43. When the valve 42isseated on the valve seat 43, fluid cannot pass therethrough, but whenthe valve 42 is unseated, gas mayflow inwardly from the lower end of thecheck valve through openings 42a, and longitudinal passages 42b forsubsequent in its open position against the action of the spring 45which tends to urge it to its seated position. Thus, the

gas is ordinarily admitted through the check valve 42 when the valve 36is unseated. However, the check valve 42 closes in the event thepressure of the gas in the casing annulus drops below the pressure ofthe liquid or fluid in the annular space 31 of the pipe string P-l sothat oil or other liquid in the pipe string P-1 is prevented fromescaping into the annulus of the well bore or casing W.

The gas under pressure in the well bore or casing W may be supplied froma well formation above the formation F-l and also above the packer X.However, in the ordinary case the annulus is supplied with pressure fromthe surface and such pressurev is maintained at a selected orpredetermined amount.

The 'valves V and V4 are both supplied with gas under pressure from thecasing annulus or well bore. To direct the gas under pressure from thecasing annulus to the gas lift valve V, a metal insert 50 having anopening 50a therein is welded or otherwise attached in the pipe stringP4 to provide a passage therethrough. A metal ring 5i having an opening51:: therein is positioned in the annular space between the pipe P-t andthe sleeve 25, and is welded or otherwise secured to'both the sleeve 25and the pipe P-l. The opening 51a is aligned with the opening 59a andalso with an opening 250 in the by-pass sleeve 25 so that fluid isdirected through such openings from the casing annulus to thelongitudinal annular area confined by the sealing elements 15 and 18between the sleeve 25 and the pipe string P. The metal ring or seal 51prevents any of the liquid or fluid which is in the pipe string P-i fromintermingling with the gas flowing through the openings 56a, SlaandZ-Sc. In effect, then, by reason of the by-pass sleeve 25 and thesealing elements 15 and 13 in sealing contact therewith, a gas chamberis provided within the bore of the pipe string P-l without causing anyloss of the gas in the liquid or fluid flowing in the pipe string P1. Aspreviously stated, the valve V illustrated in Figs. 2A and 2B issubstantially the same as the valve V-l illustrated in Fig. 4. Thus, theparts of the valve V which are identical with the parts of the valve V4;bear the same numerals except that they are followed by a prime mark.Thus, the valve V has a pressure chamber with a bellows (not shown)similar to the chamber 38 and the bellows 39 of the valve V-1 which arepositioned in the body 35' and which, together with a spring similar tothe spring 37 control the opening of the valve 36 for the inlet of gasto the pipe string P from the chamber externally thereof between thepacker sealing elements 15 and 18. Check valve 42' at the lower end ofthe assembly operates as described above in connection with check valve42 of the valve V4. The valve V is not mounted within a housing or capsuch as the housing or cap 32, but instead is mounted on the inside ofthe pipe string P with a support member or chamber 6%? which has aninner bore or opening 60a which is in iiuid communication with the inletopening 22. A threaded nipple 61 is used to connect the lower end of thevalve V to the chamber support 60.

In the use of the apparatus of this invention, and in carrying out themethod of this invention, the well packers X and Y are initially set inthe well bore or casing W above and below the well formation F-1,respectively, and thereafter the pipe string P-1 is lowered into thewell here to position same in sealing contact with the packers X and Yfor locating the perforations 12 opposite the perforations in the wellbore or casing W which are in fluid communication with the wellformation F-l. The well packer Z is then set within thepipe string P-lbelow the perforations or; openings 12, Subsequently, the. pipe string Pis lowered within the pipe string P-1 to position the perforations oropenings below the well packer Z so that the pipe string P is in fluidcommunication with the well formation F at its lower end. The wellpacker Z, together with the well packer Y, prevents any intermingling ofthe fluids in the well formations F and F-l.

Since the sealing elements and 18 are mounted with the pipe string P,they are lowered with the pipe string P as it is moved to its positionin the well bore W, but it will be appreciated that the sealing elements15 and 18 could be provided within the pipe string P-l to form the sealwith the external surface of thepipe string P, in which case, suchsealing elements 15 and 18 would be lowered separately or they could belowered with the pipe string P4. In any event, the seal by the sealingelements 15 and 18 is provided between the bypass sleeve 25 and the pipestring P so that the gas from the casing annulus is thereafter directedto the longitudinal area between seals 15 and 18.

The gas under pressure is supplied to the valves V and V-l from a commonsource, namely, the well bore or annulus therein. As previously pointedout, the gas under pressure may be supplied from a well formationpositioned above the well packer X, but ordinarily the gas underpressure is supplied from the surface of the well and is maintained at asubstantially fixed amount. The gas from the annulus in the well bore orcasing W is admitted to the pipe string P and to the annular space 31between the pipe string P and pipe string P-l separately as required byeach of the pipe strings. Thus, when the oil or other liquid in the pipestring P rises to a predetermined height above the gas lift valve V, itexerts sufficient pressure to overcome the amount of gas pressure in thebellows chamber 38 and the spring pressure 37 so that the valve V isopened and the gas is admitted through the check valve 42 and into theinterior of the pipe string P. When the level of the oil or other liquidin the pipe string P is thereafter reduced for any reason a sufficientamount to make the head of the liquid less than the pressure beingexerted to seat the valve 36, then the gas is no longer admitted throughthe valve V. The admission of the gas and the closing off of such flowof the gas to the pipe string P continues repeatedly in accordance withthe amount of oil or liquid flowing from the well formation F into thepipe string P.

The valve V-l functions in the same manner with repect to the oil orother liquid in the pipe string P-1. Therefore, when the oil or liquidin the pipe string P-1 reaches a predetermined height above the valveV-l which is sufficient to exert a greater upward pressure on the valve36 than the gas pressure in the bellows chamber 38 and the pressure ofthe spring 37, then the valve 36 is unseated and gas is admitted fromthe annulus of the casing or well bore W. Also, the valve V-1 is closedwhen the head or height of the oil or liquid in the annular space 31drops below the predetermined amount necessary to open the valve 36.Thus, the gas under pressure for lifting the oil or other liquid in bothof the pipe strings P and P-l is supplied from a common source, but thegas is introduced to each of the pipe strings P and P-1 separately inaccordance with the flow of the liquid therein.

. Although this invention has been described for dual production, itwill be evident that the invention is also applicable to the productionfrom three or more well formations. Also, although only one of each ofthe valves V and V-l have been illustrated and described herein, it willbe evident that a plurality of the valves V may be utilized inconnection with the pipe string P and a plurality of the gas lift valvesV-l may be utilized with the pipe string P-l.

- In Figs. 5, 6 and 7, the invention has been illustrated for tripleproduction. The entire assembly which is used for the dual production isused in the triple production, and the same parts bear like numerals inall figures of the drawings. Thus, the structure for establishingthefluid communication with the lower Well formations F and F-1 includesthe inner pipe string P and the outer pipe string P 1 which have the gaslift valves V and 'V-l, respectively, and the other parts as indicateddiagrammatically in Fig. 5 of the drawings. Preferably, the pipe stringsP and P-1 are angled or inclined above the packer X so as to positionthe pipe strings P and P-l to one side of the well bore W for providingadequate space to receive the third pipe string P-2. Of course, it ispossible to provide the pipe strings P and P-1 which are straightthroughout their length, in which case the packers X and Y would bemodified to receive the strings P and P-l to one side of the center ofthe well bore W.

The third pipe string P-Z is a conventional tubing string or pipe stringwhich is lowered into the well separately for establishing fluidcommunication with a third well formation F-2. The formation F4 issealed off with the well packers X and A. All of the packers used withthe apparatus of this invention are conventional in construction. Thepacker A has two openings for receiving the pipe strings P and P-1through one opening thereof and the pipe string P-2 through the otheropening thereof as best seen in Fig. 5. In such manner, the area abovethe packer A is sealed off from the well formations therebelow so thatthe gas under pressure in the well bore W above the packer A does notintermingle with the oil or other fluid being produced therefrom. A gaslift valve V-Z is mounted in the third pipe string P-2 and is preferablyidentical with the gas lift valve V mounted in the pipe string P. Thedetails of-the valve V have been described heretofore in connection withthe dualproduction assembly. It will be understood that other types ofgas lift valves may be used for the valve V-2 if desired.

It should be pointed out that the gas lift valve V-2, and all other gaslift valves which may be connected in the pipe string P-2, are also influid communication with the gas in the annulus or well bore W. Thus,all of the gas lift valves on the three pipe strings P, P1 and P-Z aresupplied with fluid under pressure from a common source, but eachpreferably operates independently or separately from the other pipestrings because the liquid or fluid level of the oil or other liquidcoming from the formations controls the injection of the gas through thegas lift valves, as previously explained in connection with the valves Vand V-l.

It is believed evident that additional tubing strings may be added forincreasing the number of well formations being simultaneously producedby gas lift, if so desired. For example, if four well formations are tobe produced simultaneously, an additional tubing string such as stringP-Z could be inserted into the well bore or casing W, or, if preferred,another dual production assembly including the tubing strings P and P-lcould be substituted for the tubing string P-Z so that four wellformations could thereby be produced.

The foregoing disclosure and description of the invention isillustrative and explanatory thereof and various changes in the size,shape and materials, as well as in the details of the illustratedconstruction, maybe made within the scope of the appended claims withoutdeparting from the spirit of the invention.

What is claimed is:

I. An apparatus adapted to be positioned in a well aid second. pipestringbelow the. comm. nicationv means in said second pipe string and.above the communication means in said first pipe. string for preventingintermingling of the oil or other liquid from the two well formations, afirst gas lift valve mounted on said first pipe string for admitting gasunder pressure into said first pipe string to effect lifting of the oilor other liquid therein, said first pipe string having an openunobstructed bore from its lower end to the first gas lift valve, asecond gas lift valve mounted on said second pipe string for admittinggas under pressure into said second pipe string to effect lifting of oilor other liquid therein, means for directing gas, under pressure in saidwell bore to each of the gas lift valves whereby each of the pipestrings is supplied with gas under pressure from a common source, saidmeans for directing gas including a seal means for sealing off an areabetween said pipe strings to prevent an intermingling of the gas passingfrom the well bore to said first gas lift valve with the oil or otherliquid. fiowing in said second pipe string, and an annular by-passopening between said first pipe string and said second pipe stringaround said seal means for the passage of the oil or other liquidupwardly in said second pipe string without being obstructed by. saidseal means.

2. The structure set forth in claim 1, wherein said first gas lift valveis positioned interiorly of said first pipe string, and said second gaslift valve is positioned exteriorly of said second pipe string, wherebyneither of said gas lift valves is positioned in the annular openingbetween the pipe strings.

3. An apparatus adapted to be positioned in a well bore for theproduction of oil or other liquid from a plurality of well formations,comprising a first pipe string disposed in said well bore, a second pipestring also disposed in said well bore surrounding said first pipestring, means establishing fluid communication between a first wellformation and the interior of said first pipe string, means establishingfluid communication between a second well formation and the annularspace between the first and second pipe strings, means for sealing ofl?an annular longitudinal area in said annular space between the first andsecond pipe strings, an annular passage means for by-passing the fluidflowing in said annular space around said longitudinal area, a first gaslift valve on said first pipe string for admitting gas into said firstpipe string from said longitudinal area, passage means sealed off fromsaid annular space connecting said longitudinal area with the annulus ofthe well bore for the fiow of gas from said annulus to said first gaslift valve, and a second gas lift valve on said second pipe string foradmitting gas from saidannulus of the well bore to the annular spacebetween the pipe strings, whereby the oil or other liquid in each pipestring is' lifted by the gas from the well bore.

4. The structure set forth in claim 3, wherein said first gas lift valveis adapted to open to admit gas to said first pipe string when theoil orother liquid in said first pipe string reaches a predetermined heightabove said first gas lift valve, and wherein said second gas lift valveis adapted to open to admit gas to the annular space between the pipestrings when the oil or other liquid in said annular space reaches apredetermined height above said second gas lift valve, whereby thefunctioning of the gas lift valves is separately controlled inconnection with each pipe string.

5. The structure set-forth in claim 3, wherein said first gas lift valveis adapted to open to admit gas to said first pipe string when the oilor other liquid in said first pipe string reaches a predetermined heightabove said first gas lift valve, and wherein said second gas-lift valveis adapted to open to admit gas to the annularspace between the pipestrings when the oil or other-liquid in said annular space reaches apredetermined height above said second gas lift valve, whereby thefunctioning of the gas lift valves is separately-controlled inconnection with each pipeistrin'g, and. each of the gas lift valveshaving a. check valve. therewith to. prevent the intermingling of theoil or.

posed in said well bore surrounding said first pipe string,

with an annular space formed therebetween, means establishing fiuidcommunication between a first well formation and the interior of saidfirst pipe string, means establishing fluid communication between asecond well formation and the annular space between the first and secondpipe strings, a by-pass sleeve positioned in said annular. space, meansconnecting said by-pass sleeve to said second pipe string to form a flowpassage between said sleeve and said second pipe string, longitudinallyspaced annular seal means disposed between said sleeve and said firstpipe string for forming a sealed-oh annular longitudinal areatherebetween, a first gas, lift valve on said first pipe string forestablishing communication between said sealed-off area and the interiorof said first pipe string, tubular means sealed off from said annularspace connecting said sealed-off area with the annulus of the well borefor the flow of gas from said annulus to said first gas lift valve, anda second gas lift valve on said outer pipe string for admitting gas fromsaid annulus of the well bore to the annular space between the pipestrings.

7. The structure set forth in claim 6, wherein the means connecting said-bypass sleeve to said second pipestring includes a plurality ofcircumferentially spaced lugs secured to the internal surface of saidsecond pipe.

string and the external surface of said sleeve.

8. The structure set forth in claim 6, wherein said seal means areresilient annular sealing elements attached to the external surface ofsaid first pipe string, whereby said seal means are adapted to bepositioned in sealing contact with the internal surface of said by-passsleeve upon the lowering of said first pipe string into position withinsaid second pipe string for production.

9. An apparatus adapted to be positioned in a well bore for theproduction of oil or other liquid from a plurality of well formations,comprising a first pipe string having means therewith establishingcommunication with a well formation producing oil or other liquid, asecond pipe string having means therewith establishing communicationwith a second well formation producing oil or 7 other liquid, said firstpipe string being positioned concentrically within said second pipestring, a third pipe string having means therewith establishingcommunication with a third well formation producing oil or other liquid,said third pipe string being separately mounted in a well adjacent tosaid first and second pipe strings, packer means between said secondpipe string and the well bore below the communication means in saidsecond pipe string, additional packer means between said first pipestring and said second pipe string below the communication means in saidsecond pipe string and above the communication means in said first pipestring, further packer means positioned in sealing contact with the wellbore and between said third pipe string and said second pipe stringbelow the communication means in said third pipe string and above thecommunication means in said second pipe string for preventingintcrmingling of the oil or other liquid from the three well formations,a first gas lift valve mounted on said first pipe string for admittinggas under pressure into said first pipe string to effect lifting of theoil or other liquid therein, said first pipe string having an openunobstructed bore below said first gas lift valve, a second gas liftvalve mounted on said second'pipe string for admitting gasunder'pressure into" said second pipe string to effect lifting of oil orother liquid therein, a third gas lift valve mounted on said third pipestring for admitting gas under pressure into said third pipe string toeifect lifting of oil or other liquid therein, and means for directinggas under pressure in said well bore to each of the gas lift valveswhereby each of the pipe strings is supplied with gas under pressurefrom a common source.

10. The structure set forth in claim 3, including a third pipe stringhaving a third gas lift valve therewith for admitting gas from saidannulus of the well bore to the interior of said third pipestring, andmeans establishl0 ing fluid communication between a third well formationand the interior of the third pipe string, whereby the oil or otherliquid from the third well formation is lifted with the gas utilized forlifting the oil or other liquid in 5 the first and second pipe strings.

Tappmeyer May 18, 1954 Davis June 8, 1954

